Geol 2312–Igneous and Metamorphic Petrology Name ___________________________ Take Home Exercise 4 DUE April 20 Mineral Reactions This exercise will familiarize you with metamorphic reactions and how to use chemographic diagrams to portray those reactions. Chapter 26 will come in handy in answering the questions below. 1. Assume the following minerals and formulas (A, B, and C are fictitious elements): a: ASiO3 b: BSiO3 c: CSiO2(OH)2 w: C2ASi2O7 x: BCSi2O6 y: A2BCSi4O12 z: ABSi2O6 In a portion of a field area, the following mineral assemblages occur in equilibrium: a-x-z b-x-z a-x-c a. Draw an accurate A-B-C compatibility diagram (projected from quartz) for this area. Assume that quartz is present in all rocks as you answer the following questions. b. Can a quartz-bearing rock contain both z and c at this grade? Why or why not?c. As we traverse up metamorphic grade, we encounter the “w-in isograd.” Show/explain how you can use the chemographics to determine the approximate (unbalanced) reaction involved with this isograd #1. Draw the new chemographic diagram for the zone above isograd #1. d. Balance the reaction. e. Illustrate the T-P dependence of the reaction on a T-P phase diagram (assuming pPH O lith2=), drawing and explaining the appropriate shape of the reaction curve (see Figure 26.2). Also label the appropriate phases on each side of the curve.f. Illustrate the T-Xfluid dependence of the reaction on a TX-CO2 phase diagram (assuming that the fluid is a CO2-H2O mixture), drawing and explaining the appropriate shape of the reaction curve. Also label the appropriate phases on each side of the curve. g. At a higher grade yet, minerals a and x are no longer stable together. Show/explain how you can use the chemographics to determine the approximate (unbalanced) reaction involved with this isograd #2 (assuming that mineral y does not become stable until higher grades). h. Balance the reaction. i. Why might some rocks show no evidence of the reaction? Be specific and refer to your diagram.j. What would you name isograd #2 and the zone above it? Why? k. Draw the compatibility diagram for the zone above isograd #2. l. As we traverse up metamorphic grade, we encounter the “y-in isograd.” Show/explain how you can use chemographics to determine the approximate (unbalanced) reaction involved with this isograd #3. m. Balance the reaction. n. Is isograd #3 a better or worse practical field isograd than isograd #2? Why?o. Draw the compatibility diagram for the zone above isograd #3. p. What are three possible reactions that may occur at the next isograd? (You need not balance them.) t. Assuming that you won’t be able to get into the field in the near future, what would you need in order to determine which of the three reactions should occur next, if at